The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having a wide viewing angle characteristic and providing high quality display.
The liquid crystal display device is a flat display device having excellent features of being thin, light in weight and low in power consumption. However, the liquid crystal display device has a shortcoming of being large in “viewing angle dependence” in which the display state changes with the direction in which the display device is observed. A main cause for the large viewing angle dependence of the liquid crystal display device is that liquid crystal molecules having uniaxial optical anisotropy are oriented uniformly in the display plane.
To improve the viewing angle characteristic of the liquid crystal display device, an orientation division method is effective, in which a plurality of regions different in orientation states are formed in each picture-element region. Various techniques have been proposed to implement this method. Among these, a technique disclosed in Japanese Laid-Open Patent Publication No. 6-301036 and No. 2000-47217 and a technique called MVA disclosed in Japanese Laid-Open Patent Publication No. 11-242225 are considered as typical techniques for implementing the orientation division on vertical alignment mode liquid crystal display devices.
In the technique disclosed in Japanese Laid-Open Patent Publication No. 6-301036 and No. 2000-47217, an inclined electric field is generated by forming slits (openings) for an electrode, to control the orientation direction of liquid crystal molecules with the generated inclined electric field.
In the MVA technique disclosed in Japanese Laid-Open Patent Publication No. 11-242225, a pair of substrates (for example, a TFT substrate and a color filter substrate) opposed to each other via a liquid crystal layer have protrusions, depressions or slits (openings of an electrode) formed on their surfaces facing the liquid crystal layer, to thereby realize the orientation division.
As the type of the orientation division of each picture-element region, there are comparatively simple types, such as two-division type in which liquid crystal molecules in each picture-element region are oriented in two directions and four-division type in which they are oriented in four directions, and comparatively complicate types, such as infinite-division type in which liquid crystal molecules are oriented in all directions and the type in which liquid crystal molecules are twisted in a liquid crystal layer.
From the standpoint of achieving equal display characteristics in all directions, liquid crystal molecules are preferably oriented in as many directions as possible in each picture-element region. In general, orientation in four or more directions is considered providing sufficient display quality.
However, as a result of examinations by the present inventors, it was found that the techniques disclosed in Japanese Laid-Open Patent Publication No. 6-301036, No. 2000-47217 and No. 11-258606 had the following problem. Although the azimuthal angle dependence of the display characteristics can be improved by these techniques, the display characteristics obtained when the display device is observed from the front is greatly different from that obtained when it is observed obliquely. Therefore, the gray-scale characteristic greatly varies with the angle at which the observer views the display plane, and this makes the observer feel unnatural.